java的循环问题
每当我运行此循环时:java的循环问题,java,eclipse,for-loop,nested-loops,Java,Eclipse,For Loop,Nested Loops,每当我运行此循环时: System.out.println("How many gerbils are in the lab?"); int population = keyboard.nextInt(); Gerbil[] gerbil = new Gerbil[population]; for (int i=0; i<population; i++){ gerbil = new Gerbil[population]; idnumber:
System.out.println("How many gerbils are in the lab?");
int population = keyboard.nextInt();
Gerbil[] gerbil = new Gerbil[population];
for (int i=0; i<population; i++){
gerbil = new Gerbil[population];
idnumber:
for
(int b = 0; b<population; b++){
System.out.println("What is the id number of gerbil " + (b+1));
String idnumberx = keyboard.next();
if (b>0){
for (int c = 0; c<gerbil.length; c++){
if (idnumberx.equals(gerbil[c].getId())){
System.out.println("Repeat, try again");
c--;
}
else {
return;
}
}
}
}
第57行是这样的:if(idnumberx.equals(沙鼠[c].getId()){
基本上,我的程序要求用户输入x个沙鼠的id。如果其中一个沙鼠id与以前的id匹配,则输出应为
repeat, try again
以下是我的代码的其余部分供参考:
package assignment4;
import java.util.Scanner;
import java.util.Arrays;
import assignment4.Gerbil;
public class Assignment4 {
public static int population;
public static int[] foodeats;
public static int types;
public static String idnumberx;
public static String nicknamex;
public static String g;
public static String gerbilId;
public static Gerbil[] gerbil;
public static String amountoffoodeaten;
public static String gerbilsearch;
public static String thisgerbil;
public static String foodname;
public static int[] totalfood;
public static food[] food;
public static int maximum;
public static boolean bite;
public static boolean escape;
public static void main(String args[]){
Scanner keyboard = new Scanner(System.in);
System.out.println("How many types of food do the gerbils eat?");
int F = keyboard.nextInt();
food = new food[F];
for
(int a = 0; a<food.length; a++){
System.out.println("Name of food number " + (a+1));
foodname = keyboard.next();
System.out.println("Max amount of food " + (a+1));
maximum = keyboard.nextInt();
food[a] = new food(foodname, maximum);
}
System.out.println("How many gerbils are in the lab?");
int population = keyboard.nextInt();
Gerbil[] gerbil = new Gerbil[population];
for (int i=0; i<population; i++){
gerbil = new Gerbil[population];
idnumber:
for
(int b = 0; b<population; b++){
System.out.println("What is the id number of gerbil " + (b+1));
String idnumberx = keyboard.next();
if (b>0){
for (int c = 0; c<gerbil.length; c++){
if (idnumberx.equals(gerbil[c].getId())){
System.out.println("Repeat, try again");
c--;
}
else {
return;
}
}
}
}
System.out.println("What is the name for gerbil " + (i+1));
String nicknamex = keyboard.next();
foodeats = new int[F];
for
(int c = 0; c<foodeats.length; c++){
System.out.println("how much " + food[c].foodname + " does " + nicknamex + " eat");
int gerbileats = keyboard.nextInt();
foodeats[c] = gerbileats;
if (gerbileats > maximum){
do{
System.out.println("You stoopid, try again");
c--;
}
while (gerbileats <= maximum);
}
}
for
(int d = 0; d<population; d++){
System.out.println("Does " + nicknamex + " bite? Please enter True or False");
String doesitbite = keyboard.next();
if (doesitbite.equalsIgnoreCase("true")){
bite = Boolean.parseBoolean(doesitbite);
break;
}
else if (doesitbite.equalsIgnoreCase("false")){
bite = Boolean.parseBoolean(doesitbite);
break;
}
else
System.out.println("Repeat, try again");
d--;
}
for
(int d = 0; d<population; d++){
System.out.println("Does " + nicknamex + " escape? Please enter True or False");
String doesitescape = keyboard.next();
if (doesitescape.equalsIgnoreCase("true")){
escape = Boolean.parseBoolean(doesitescape);
break;
}
else if (doesitescape.equalsIgnoreCase("false")){
escape = Boolean.parseBoolean(doesitescape);
break;
}
else
System.out.println("Repeat, try again");
d--;
}
gerbil[i] = new Gerbil(idnumberx, nicknamex, foodeats, bite, escape);
}
while (true){
System.out.println("What would you like to know?");
String question = keyboard.nextLine();
String search = "search";
String average = "average";
String end = "end";
String restart = "restart";
if (question.equalsIgnoreCase(search)){
new Assignment4().searchForGerbil();
}
else
if (question.equalsIgnoreCase(average)){
//new Assignment4().averageFood();
}
else
if (question.equalsIgnoreCase(end)){
System.exit(0);
}
else
if (question.equalsIgnoreCase(restart)){
new Assignment4().main(args);
}
else
System.out.println("Try again");
}
}
public static void searchForGerbil()
{
System.out.println("Please type in a gerbil lab ID");
Scanner keyboard = new Scanner(System.in);
String searchgerbil = keyboard.next();
boolean found = false;
int i = 0;
int location = 0;
for (i = 0; i <gerbil.length; i++){
if ( searchgerbil.equals(gerbil[i].getId()))
{
found = true;
location = i;
break;
}
else
{
found = false;
}
}
if (found = true){
System.out.println(gerbil[location]);}
else {
System.out.println("Gerbil " + searchgerbil + " does not exist");
}
}
//return everything;
//
}
这是你的问题:
Gerbil[] gerbil = new Gerbil[population];
for (int i=0; i<population; i++){
gerbil = new Gerbil[population]; // reinitilizing array
沙鼠[]沙鼠=新沙鼠[种群];
对于(int i=0;i这是您的问题:
Gerbil[] gerbil = new Gerbil[population];
for (int i=0; i<population; i++){
gerbil = new Gerbil[population]; // reinitilizing array
沙鼠[]沙鼠=新沙鼠[种群];
对于(int i=0;i
您的问题是gerbil[c]
为null。这是因为Java中的数组默认将其所有值初始化为null
。您可以通过检查null来修复此问题
for (int c=0;c<gerbil.length;c++) {
if (gerbil[c] == null) // Tests if null.
break; // If null exit loop.
if (idnumberx.equals(gerbil[c].getId())) {
System.out.println("Repeat, try again");
c--;
} else {
return;
}
}
for(int c=0;c
您的问题是gerbil[c]
为null。这是因为Java中的数组默认将其所有值初始化为null
。您可以通过检查null来修复此问题
for (int c=0;c<gerbil.length;c++) {
if (gerbil[c] == null) // Tests if null.
break; // If null exit loop.
if (idnumberx.equals(gerbil[c].getId())) {
System.out.println("Repeat, try again");
c--;
} else {
return;
}
}
for(int c=0;c您正在引用一个空数组。沙鼠数组中没有沙鼠类的对象。因此,下面的条件将引发NullPointerException:
if (idnumberx.equals(gerbil[c].getId())){
我认为您应该更改下面的第(49)行,创建一个沙鼠类的对象并将其放入数组中
gerbil = new Gerbil[population];
您正在引用一个空数组。沙鼠数组中没有沙鼠类的对象。因此,下面的条件将引发NullPointerException:
if (idnumberx.equals(gerbil[c].getId())){
我认为您应该更改下面的第(49)行,创建一个沙鼠类的对象并将其放入数组中
gerbil = new Gerbil[population];
Java中的数组索引基于0
,而不是1
。这应该做什么?Java中的数组索引基于0
,而不是1
。这应该做什么?